ATLANTA – The US Centers for Disease Control and Prevention is now aware of 153 possible cases of severe lung disease in 16 states that could be caused by vaping, the agency said Wednesday in an update to a multi-state investigation.

The cases — reported from June 28 to August 20, 2019 — have popped up in California, Connecticut, Florida, Illinois, Indiana, Iowa, Minnesota, Michigan, North Carolina, New Jersey, New Mexico, New York, Pennsylvania, Texas, Utah and Wisconsin. They have primarily affected adolescents and young adults.

This is an increase from Saturday, when CDC announced it was looking into 94 possible cases in 14 states. At the time, a CNN surveyof state health departments concluded there were more than 120 cases in at least 15 states.

There are no known deaths at this time, the agency said. In many cases, patients have gradually had difficulty breathing and chest pain before being hospitalized. A number of patients have also reported using products with tetrahydrocannabinol, known as THC, the psychoactive substance within cannabis.

“While some cases in each of the states are similar and appear to be linked to e-cigarette product use, more information is needed to determine what is causing the illnesses,” the CDC said.

The agency added it’s working with state health departments and the US Food and Drug Administration to figure out which products might have been used and facilitate laboratory testing. In an email Friday, the CDC urged doctors to collect information and samples from patients who might fit a similar description.

A tough condition to track

The Minnesota Department of Health reported last week that some patients were hospitalized for “multiple weeks,” in some cases ending up in the intensive care unit. They came in with symptoms including shortness of breath, fever, cough, vomiting, diarrhea, headache, dizziness and chest pain.

Dr. Emily Chapman, chief medical officer at Children’s Minnesota, which reported four cases, said in a statement last week that these illnesses are tricky to diagnose because they can start off looking like a common infection before leading to more serious complications.

They are also tricky to track, experts say, because vaping-related lung disease is not a condition that’s mandatory to report. Some health departments told CNN they don’t track this data.

Still, states are putting out notices in hopes that doctors will notice the clues and ask the right questions. In Colorado, Georgia and Kansas, health officials have tried to look for cases by analyzing data from emergency departments.

“There is no diagnostic code … for lung diseases related to vaping. So it’ll be hard to follow and track,” Dr. Humberto Choi, a pulmonologist and critical care specialist at the Cleveland Clinic, previously told CNN.

Choi said he had seen several cases himself over the last several months — and he suspects there were others who didn’t think of vaping as a potential cause.

“People had the impression that vaping was something safe,” Choi said. “They don’t connect new symptoms with vaping.”

Choi’s state of Ohio, however, is not one of the states where health departments or the CDC are currently reporting potential cases.

“It’s hard to tell what to expect in these cases because it’s something new,” Choi said.